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Tripping the light fantastic

Proponents of laser-assisted launch systems might also like to consider their electricity consumption. Dr Jordin T Kare's "modular laser launcher" would require "hundreds or thousands" of ground-based lasers, "each of which transmits a relatively small amount of power to a laser-powered rocket vehicle".

Dr Jordin T Kare's modular laser launch system

Scientists have various flavours of laser propulsion systems on the menu. These include: ablative, which uses a pulsed laser aimed at a solid metal fuel, burning off a thrust-producing plasma; pulsed plasma, where the breakdown of a gas such as air, and the resulting expanding plasma, provides thrust; and laser electric propulsion - the conversion of the beam's energy into electricity, for example via photovoltaic cells.

In 2003, NASA hailed the world's first laser-powered aircraft, which used just such photovoltaic cells collecting energy from a remote laser to drive a small electric motor.

NASA's laser-powered aircraft

Such aircraft will fly as long as their panels are targeted by the laser, but that's not really practical for high-altitude operation at long distance. Dr Kare's hybrid solution is to use laser energy to heat a launch vehicle's fuel via a heat exchanger. His multi-laser approach would appear to give a good chance of continuous power delivery, albeit at the cost of a massive ground operation.

Still, the potential environmental impact of vast laser farms spreading across the landscape probably wouldn't be as great as that of using nuclear power to get into space, as suggested by Project Orion scientists.

Orion

In 1958, the US started work on a nuclear pulse propulsion system - simply a series of nuclear detonations delivering massive thrust - was theoretically capable of lifting a 3,629 tonne Orion vehicle plus a 1,451 tonne payload into LEO.

The spaceship's massive size was dictated by the smallest nuclear device available, of which 800 would be required to reach LEO. Bombs would be continually ejected at the rate of around one per second through a "pusher plate", explode, and propel the vehicle. The damped pusher plate smoothed the delivery of thrust to the spacecraft above.

Very hot stuff: The Orion propulsion system

The yield of each bomb was 0.14 kt - a modest amount but the total for a launch was 112 kt, greater than that of a W76 thermonuclear warhead.

Concerns over fallout led to loss of political support for the programme; the 1963 Partial Test Ban Treaty finally killed it. The technology still has its supporters as a means for interplanetary travel, on the assumption it's used once spacecraft are a safe distance from Earth.

We'll wrap up this look at space launch technologies with what is very much flavour of the month in get-me-off-this-planet circles: the space elevator.

Requiring nothing more than a cable tethered to the Earth's surface and extending beyond geostationary orbit with a "counterweight" at the end, the current space tether concept is the offspring of the space tower proposal to build our way into orbit.

As gravity decreases up the length of the cable, the centrifugal forces increase. The balance of the two keeps the cable taut and the upper end in a fixed position above the surface.

Having got our long rope to the stars in place, we can then ride elevators up the cable into orbit, from where our conquest of the galaxy is assured.

Going up: NASA's concept for a space elevator

NASA has taken a keen interest in space elevators, as has the private sector.

Japan's Obayashi Corporation has declared it will be able to whisk passengers upwards by 2050, thanks to carbon nanotube technology.

The Obayashi Corporation's space elevator

The carbon nanotube is vital to the space elevator. When Russian scientist Konstantin Tsiolkovsky first considered extending the Eiffel Tower into space in 1895, he was doubtless aware that the weight of the beast would simply crush it at the base.

Now that this compression structure plan has given way to a tensile structure model, the weight of the cable still poses a big problem. Lightweight carbon nanotubes are the solution, scientists say, and perhaps within a decade or so we'll be in a position to begin weaving our space cable.

Until that happens, we'll leave you with one last theoretical means of escaping Earth's pull and Wernher von Braun's long shadow, which is to our minds at least as feasible as the space elevator...